Vibration transducer

ABSTRACT

Vibration transducer having a sealed capsule secured concentrically to an integral soft iron pole piece. An elongate bar magnet is slidably mounted in the capsule and has substantially coincident magnetic and mechanical axes. Suitable means is mounted within the capsule and engages opposite ends of the bar magnet and serves to yieldably retain the bar magnet in a predetermined position within the capsule. The capsule is filled with gas. The capsule and bar magnet are formed in such a manner that there is provided a passage for the controlled flow of gas from one end of the magnet to the other end of the magnet as the magnet moves from its predetermined position. Electromagnetic coil means is provided for detecting the movement of the magnet within the capsule.

Umte States 1 3,633,053

[72] Inventor Rex B. Peters 3,453,573 7/1969 Kyle 310/15 X Concord,Calif. 3,463,946 8/1969 Zimmerman 310/15 [21] App]. No. 47,272 3,504,3203/1970 Engdahl et a1. 310/15 X 525: te d 52:7 Primary Examiner-D. F.Duggan Assignee symombomer Corporafion AttorneyF1ehr, Hohbach, Test,Albntton & Herbert Concord, Calif.

ABSTRACT: Vibration transducer having a sealed capsule [54] VIBRATIONTRANSDUCER secured cgncentncallv tol aln Iirlitegral soft1 lronhpolePICTC. A;

13 Claims snmwing Figs. elongate ar magnet 15. st a y mounte in t ecapsu e an has substantially colncident magnetic and mechanical axes.

U.S. means mounted within the capsule and engages op- 340/177 73/71-2posite ends of the bar magnet and serves to yieldably retain ll. the barmagnet in a predetennined position the capsule [50] Field 0' Search310/15, 30, The capsule is filled with gas, The capsule and bar magnetarc 336/132, 30 formed in such a manner that there is provided a passagefor the controlled flow of gas from one end of the magnet to the [56]References cued other end of the magnet as the magnet moves from itsUNITED STATES PATENTS predetermined position. Electromagnetic coil meansis pro- 3,100,292 8/1963 Warner, Jr. et a1. 340/17 vided for detectingthe movement of the magnet within the W s. 9 9 .3 IE6 EQ"Y1-; ..s. lX53... capsuleat o M a /l /5 j j 7 1A /7 its- 32 33 4/ s 45 /2/ L 3] Q/J Z? If, r 2/ v INVENTOR.

Rex B. Peters Z;Z1%, W324 mgm VIBRATION TRANSDUCER BACKGROUND OF THEINVENTION Vibration transducers have heretofore been provided which havebeen utilized sliding bar magnets. Such vibration transducers have beenunsatisfactory because very high friction levels were encountered insuch transducers which greatly limited their useful life. There is,therefore, a need for a new and improved vibration transducer.

SUMMARY OF THE INVENTION AND OBJECTS The vibration transducer consistsof a sealed capsule which has an elongated bore therefore, a need for anew and improved vibration transducer.

SUMMARY OF TI-IE INVENTION AND OBJECTS The vibration transducer consistsof a sealed capsule which has an elongate bore therein. A cylindricalsoft ion pole piece is secured to the capsule to become an integral partthereof. An elongate bar magnet is slidably mounted in the capsule.Yieldable means is mounted within the capsule and engages opposite endsof the bar magnet and serves to yieldably retain the bar magnet in apredetermined position in the bore in the capsule. The bore in thecapsule is filled with gas. The capsule and the bore are formed in sucha manner as to provide a passage from one end of the magnet to the otherend of the magnet to permit a controlled flow of gas from one end of themagnet to the other end of the magnet as the magnet moves in the bore.An electromagnetic coil is provided for sensing movement of the magnetin the capsule.

In general, it is an object of the present invention to provide avibration transducer which operates with accuracy and which has a longlife.

Another object of the invention is to provide a transducer of the abovecharacter which is gas damped in such a manner as to obtainsubstantially linear damping.

Another object of the invention is to provide a transducer of the abovecharacter in which the magnet is precisely centered on the transduceraxis.

Another object of the invention is to provide a transducer of the abovecharacter in which the magnet has substantially coincident magnetic andmechanical axes.

Another object of the invention is to provide a transducer of the abovecharacter in which the part in which the capsule containing the magnetcan be readily replaced.

Another object of the invention is to provide a transducer of the abovecharacter which is a self-generating device.

Another object of the invention is to provide a transducer of the abovecharacter which has a relatively long life.

Another object of the invention is to provide a transducer of the abovecharacter which can be disassembled and reassembled without thenecessity of realignment.

Additional objects and features of the invention will appear from thefollowing description in which the preferred embodiment is set forth indetail in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a top plan view of avibration transducer incorporating the present invention.

FIG. 2 is a side elevational view looking along the line 22 of FIG. 1.

FIG. 3 is a cross-sectional view taken along the line 33 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The vibration transducer shownin the drawings consists of a case 11 formed of a suitable material suchas steel which is provided with a large flanged portion 110 at is lowerextremity which has therein a plurality of holes 12 to permit thevibration transducer to be bolted to the object on which it is tomeasure vibration. The case 11 is provided with a large bore 13 which isadapted to receive a cap assembly 14. The cap assembly 14 carries acapsule assembly 16 and a coil assembly 17.

The capsule assembly 16 consists of an elongate openended cylindricaltube 21 which is provided with a radially extending flange portion 21aat one end of the same. The tube 21 is formed of suitable nonmagneticmaterial such as austenitic stainless steel. The tube 21 is providedwith a cylindrical bore 23 which extends through the tube. Plugs 24 and26 formed of a nonmagnetic material are mounted in the ends of the tube21 and seal the ends of the tube so that a hermetically sealed chamber27 is provided within the tube. The plugs 24 and 26 limit the magneticcircuit as hereinafter described. The plugs 24 and 26 are provided withinwardly extending bosslike portions 240 and 260, respectively, whichare centered with respect to the longitudinal axis of the bore 23. Acylindrical bar magnet is disposed within the bore 23 and is sized andis provided with a polished surface so that it can readily slide withinthe bore 23. In other words, there is not a tight fit between the magnetand the sidewalls of the tube 21.

Means is provided within the capsule for engaging opposite ends of themagnet 28 so that the magnet is yieldably retained in a predeterminedlongitudinal position within the tube 21. As can be seen, such meansconsists of a pair of coil springs 29 which engage the bosslike portions24a and 26a of the end plugs 24 and 26, and similarly engage bosslikeportions 28a provided on the ends of the bar magnet. The chamber 27 isfilled with a dry gas such as a nitrogen during manufacture of thecapsule assembly. This can be accomplished in a number of ways. Forexample, a hole can be drilled in one of the plugs 24 and the dry gasintroduced through this hole and then the hole can be sealed. The tube21 and the magnet 28 are formed in such a manner so that there isprovided a passage which will permit the controlled flow of the gas fromone end of the mag net to the other when the magnet shifts its positionlongitudinally of the bore 23.

Such means takes the form of a pair of flats 31 provided on the barmagnet 28 and extending the length thereof. The flats 31 arediametrically opposed for purposes of symmetry. The gas passages whichare formed in this manner are so proportioned that substantially lineardamping is obtained. The criteria for obtaining this linear damping are:

a. the gas passages must be sufficiently long so that the kinetic energyof the flowing gas is small, i.e., less than 10 percent compared to thefriction losses in the passages.

b. the gas passages must produce a sufficiently small Reynolds numberranging from 0 to 3,000 to assure substantially laminar flow.

The bar magnet 28 can be formed of any suitable material. However, it isessential that the magnet axis and the mechanical axis of the bar magnet28 be substantially coincident. By way of example, it has been foundthat Alnico 5 is a 'material which has sufficient uniformity for use insuch a magnet so that the magnet axis is substantially coincident withthe mechanical axis of the magnet.

Great care is taken in the manufacture of the parts which make up thecapsule assembly 16. The end plugs 24 and 26 are also preciselypositioned and are welded in place by suitable means such as electronicwelding. A cylindrical sleeve 32 having an axially aligned bore 33therein is provided and is formed of soft iron so that it can serve as apole piece. The tube 21 is precisely positioned within the bore by a jigand then is welded to the cylindrical sleeve 32 by suitable means suchas electron welding. As can be seen, the sleeve 32 is welded to theflange portion 210 of the tube 21. The sleeve 32 is also provided with aflange portion 32a. The sleeve 32 with The cap assembly 14 consists of acap 36 formed of a suitable nonmagnetic material such as austeniticstainless steel. The cap 36 is provided with an elongate cylindricalextension 36a which is to fit within the sleeve 32. The extension 36a isprovided with a large bore 37 which is adapted to receive the capsuleassembly 16 carried by the sleeve 32. The cylindrical extension 360carries electromagnetic coil means for sensing movement of the magnetlongitudinally of the bore 23. The electromagnetic coil means consistsof a pair of cylindrical windings 38 and 39 which are wound intorecesses M provided in the cylindrical extension 3611. The windings 38and 39 are formed of a suitable material such as insulated copper wire.As can be seen, the windings 38 and 39 encircle the cylindricalextension 36a and the capsule assembly 16.

' The winding 38 and 39 are cylindrical and have a combined length whichis substantially greater than the length of the magnet and, in fact,have a combined length which is great enough to accommodate the possiblelimits of travel of the magnet 28 and the fringing field created by themagnet. The magnet 28 itself has to be long enough so that the center ofeach of the windings is sufficiently removed from the end of the windingso that excessive amounts of the fringing field are not present in theother half of the winding when the magnet is at one extreme end of itstravel.

The two windings 38 and 39 in fact form one coil and thus each serves asone-half of the coil. The two windings 38 and 39 are wound in oppositedirections so that the outputs from the two halves will be additive. Thetwo windings 38 and 39 are interconnected through a slot 42 extendingbetween the two recesses 41. The ends of the wires of the windings 38and 39 extend upwardly through the hole 43 provided in the flangeportion 32a of the sleeve 32 and are secured to a pair of terminals 44.The terminals extend upwardly through a hole 46 provided in the cap 36and into a large bore 47 also provided in the cap 36. The terminals 44extend through holes 48 provided in the threaded connector 49. Theterminals 44 are insulated from the connector 49 by a block 51 ofinsulating material mounted in the connector 49. The connector 49 isseated in a bore 52 provided in the cap 36.

The cap assembly 14 is secured to the case 11 by a plurality ofcapscrews 54. A seal ring or washer 56 is provided between the cap 36and the flange portion 32a of the sleeve 32. It' can be seen that thescrews 54 secure the cap assembly 14, the sleeve 32 which carries thecapsule assembly 16, and the case 11 into a unitary assembly.

Operation and use of the vibration transducer may now be brieflydescribed as follows. Let it be assumed that the vibration transducerhas been mounted in apparatus such as a jet engine in which it isdesired to monitor vibration. This is accomplished by bolting the flange1 la of the case to the part on which vibration is to be monitored.Since the magnet has a mass, vibration of the case 11 will cause themagnet to shift back and forth or, in other words, move rectilinearlywithin the bore 23 against the yieldable force of the springs 29 by anamount which is directly proportional to the vibration which is beingmeasured. As the magnet 28 shifts back and forth within the bore, themagnetic lines of force from each end of the magnet will cut theadjacent turns of the windings 38 and 39 to cause the generation of anelectrical signal which represents the velocity of movement of themagnet within the bore. This velocity signal is converted from velocityto displacement by the use of electronics which performs an integrationstep. This displacement is then displayed on a meter or other suitableindicating means to give an indication of the vibration which is beingmeasured. The output from the coils 38 and 39 has a very low electricalimpedance with a relatively high signal level which permits the signalto be passed through long cables as, for example, from engine pods ofjet engines on aircraft to the cockpit of the aircraft without providingadditional electronics at the engine.

The construction of the vibration transducer is relatively simple and isformed of materials so that it can accommodate extremely hightemperatures such as those which are encountered in the operation of jetengines.

It has been found that a vibration transducer constructed in the mannerherein described has very little wear. This in part is due to the factthat substantially all of the cylindrical surface of the bar magnet 28,except for the flats 31, is used as a hear ing surface and therebyreduces rattling contact stresses which could cause undesirablebrinelling" of the surface 23 of the tube 21. This reduction in wear isalso due to the fact that very accurate concentricity has been obtainedin the manufacture of the vibration transducer which minimizes any sideloading on the magnet. In the event that the vibration transducer ismounted in its side, the side loading of the magnet against the sidewallof the tube in which it is travelling is l G. When the vibrationtransducer is mounted in a vertical position, it is believed that theside loading is not more than one-quarter G. This has been accomplishedby the use of a number of features. For example, the magnet 28 isconstructed in such a manner that the magnetic axis is as close aspossible to the mechanical axis of the magnet. This ensures that therewill be no substantial nonuniformity in the magnetic field which couldcause side loading of the magnet against the tube in which it istravelling. A good return path has been provided for the magnetic fieldsby the soft iron pole piece in the form of the sleeve 32. All theseparts are precisely centered with respect to each other so that themagnet 28 is automatically placed in the center of the magnetic polepiece structure so that in effect the magnet is in neutral equilibrium.In other words, the magnet is being attracted by equal forces in alldirections to the magnetic pole piece structure forming the return path.This has the effect of reducing the friction to such a low level that itapproximates a situation in which there is no magnetic pole piecestructure surrounding the magnet.

The vibration transducer also has excellent characteristics because ofthe gas damping which is utilized. As pointed out previously, gaspassages are provided which permit the control of the flow of gas fromone end of the chamber to the other when the magnet moves within thechamber 27. The passages have been formed in such a manner that thedamping is linear which makes it possible to obtain much more consistentlowfrequency performance from the vibration transducer. The damping is,therefore, accomplished by air friction between the wall of the tube 21and the flats 31 provided on the magnet 28.

The bosslike portions 28a and 26a are adapted to be engaged by thebosslike portion 28a provided on the magnet and in combination inaddition to serving as a means for retaining the ends of the springs 29serve as stops to prevent flattening of the coil springs 29 in the eventof very severe vibrations being encountered by the vibration transducer.

The vibration transducer is constructed in such a manner that in theevent if necessary to replace certain parts, it can be readilyaccomplished with a minimum of labor expense.

In the event for some reason it is desirable to replace the capsuleassembly 16, this capsule assembly 16 which has a low labor content canbe readily removed and replaced. Integra tion of the soft iron polepiece so that it forms a part of the capsule assembly 16 permitsdisassembly without breaking the magnetic circuit. This means thatcapsule assemblies can be removed and replaced without affectingcalibration accuracy. This makes it possible to ship precalibratedcapsules for replacement in the field where calibration facilities arenot available.

It is apparent from the foregoing that there has been provided avibration transducer which has many advantages. It is a self-generatingdevice. It has low wear and can be readily disassembled and certainparts replaced. All parts which are required to be accurately concentricare contained in a single weldment, so that no special alignment isneeded during field assembly.

I claim:

ll. In a vibration transducer, a capsule assembly comprising a sealedcapsule having an elongate bore therein, and a cylindrical soft ironpole piece secured to the capsule exterior of and substantiallyconcentric with the capsule, said capsule including an elongate barmagnet formed solely of magnetic material slidably mounted in saidcapsule, yieldable means mounted within the capsule and engagingopposite ends of the bar magnet and serving to yieldably retain the barmagnet in a predetermined position within the capsule, a gas fillingsaid capsule, said capsule and said magnet being formed to provide a gaspassage therebetween to permit the controlled flow of gas from one endof the capsule to the other end of the capsule past the bar magnet, saidgas passage extending only over a portion of the circumferences of thebar magnet, a case enclosing said capsule and electromagnetic coil meansin said case for sensing movement of said bar magnet in said capsule.

2. A transducer as in claim 1 wherein said passage for the flow of gasis formed so that substantially linear damping of the magnet isobtained.

3. A transducer as in claim 1 wherein said electromagnetic coil means isin the form of a pair of windings with the windings wound in oppositedirections so that their outputs are additive.

4. A transducer as in claim 3 wherein said electromagnetic coil meanshas a length which is greater than the length of the magnet and theextremes of travel of the magnet within the capsule.

5. A transducer as in claim 3 wherein said gas passage is formed bydiametrically opposed recesses in said magnet.

6. A transducer as in claim 1 wherein said soft iron pole piece issecured to said capsule assembly.

7. A transducer as in claim 1 wherein said magnet and the capsuleassembly containing the magnet are precisely centered with respect toeach other so that side loading on the magnet is minimized.

8. In a vibration transducer, a case, a bore in said case, a sleeve ofsoft iron mounted in said bore and forming a pole piece, a tube carriedby said sleeve and secured to said sleeve, said tube having a boredepending longitudinally thereof, a bar magnet formed solely of magneticmaterial slidably mounted in said bore, a pair of end plugs mounted insaid tube and serving to seal said tube so that there is providedtherein a hermetically sealed chamber, a gas filling said chamber, meansengaging said end plugs and the ends of said magnet for yieldablyretaining said magnet in a predetermined position in said bore, a capcarried by said case, said cap having a cylindrical extension having abore therein receiving said tube and a coil wound on said cylindricalextension and encircling said tube, said tube and said magnet beingformed so as to provide a gas passage therebetween from one end of thechamber to the other and extending over only a portion of the surface ofthe magnet to permit the flow of gas in a controlled manner from one endof the chamber to the other past the magnet.

9. A transducer as in claim 8 wherein said sleeve and said tube areprecisely positioned with respect to each other so that the magnet isuniformly attracted to all parts of the same to thereby reduce the sideloading on the magnet.

10. A transducer as in claim 8 wherein said coil has a length which issubstantially greater than the magnet and the limits of travel of themagnet within the tube.

11. A transducer as in claim 10 wherein said coil is in the form of apair of windings wound in opposite directions and which are connected toeach other so that outputs from the same are additives.

12. A transducer as in claim 8 wherein the passages are formed byrecesses formed on the magnet and extending longitudinally of themagnet.

13. A transducer as in claim 8 wherein said end plugs are provided withcentered bosslike portions and wherein said magnet is also provided withcentered bosslike portions on opposite ends of the same and wherein saidmeans engaging the end plugs and the ends of the magnet comprises a pairof coil springs mounted on said bosslike portions of the end plugs andthe bosslike portions of the magnets, said bosslike portions on saidplugs and said magnets being adapted to engage each other and to serveas stops to prevent flattening of said coil springs.

1. In a vibration transducer, a capsule assembly comprising a sealedcapsule having an elongate bore therein, and a cylindrical soft ironpole piece secured to the capsule exterior of and substantiallyconcentric with the capsule, said capsule including an elongate barmagnet formed solely of magnetic material slidably mounted in saidcapsule, yieldable means mounted within the capsule and engagingopposite ends of the bar magnet and serving to yieldably retain the barmagnet in a predetermined position within the capsule, a gas fillingsaid capsule, said capsule and said magnet being formed to provide a gaspassage therebetween to permit the controlled flow of gas from one endof the capsule to the other end of the capsule past the bar magnet, saidgas passage extending only over a portion of the circumferences of thebar magnet, a case enclosing said capsule and electromagnetic coil meansin said case for sensing movement of said bar magnet in said capsule. 2.A transducer as in claim 1 wherein said passage for the flow of gas isformed so that substantially linear damping of the magnet is obtained.3. A transducer as in claim 1 wherein said electromagnetic coil means isin the form of a pair of windings with the windings wound in oppositedirections so that their outputs are additive.
 4. A transducer as inclaim 3 wherein said electromagnetic coil means has a length which isgreater than the length of the magnet and the extremes of travel of themagnet within the capsule.
 5. A transducer as in claim 3 wherein saidgas passage is formed by diametrically opposed recesses in said magnet.6. A transducer as in claim 1 wherein said soft iron pole piece issecured to said capsule assembly.
 7. A transducer as in claim 1 whereinsaid magnet and the capsule assembly containing the magnet are preciselycentered with respect to each other so that side loading on the magnetis minimized.
 8. In a vibration transducer, a case, a bore in said case,a sleeve of soft iron mounted in said bore and forming a pole piece, atube carried by said sleeve and secured to said sleeve, said tube havinga bore depending longitudinally thereof, a bar magnet formed solely ofmagnetic material slidably mounted in said bore, a pair of end plugsmounted in said tube and serving to seal said tube so that there isprovided therein a hermetically sealed chamber, a gas filling saidchamber, means engaging said end plugs and the ends of said magnet foryieldably retaining said magnet in a predetermined position in saidbore, A cap carried by said case, said cap having a cylindricalextension having a bore therein receiving said tube and a coil wound onsaid cylindrical extension and encircling said tube, said tube and saidmagnet being formed so as to provide a gas passage therebetween from oneend of the chamber to the other and extending over only a portion of thesurface of the magnet to permit the flow of gas in a controlled mannerfrom one end of the chamber to the other past the magnet.
 9. Atransducer as in claim 8 wherein said sleeve and said tube are preciselypositioned with respect to each other so that the magnet is uniformlyattracted to all parts of the same to thereby reduce the side loading onthe magnet.
 10. A transducer as in claim 8 wherein said coil has alength which is substantially greater than the magnet and the limits oftravel of the magnet within the tube.
 11. A transducer as in claim 10wherein said coil is in the form of a pair of windings wound in oppositedirections and which are connected to each other so that outputs fromthe same are additives.
 12. A transducer as in claim 8 wherein thepassages are formed by recesses formed on the magnet and extendinglongitudinally of the magnet.
 13. A transducer as in claim 8 whereinsaid end plugs are provided with centered bosslike portions and whereinsaid magnet is also provided with centered bosslike portions on oppositeends of the same and wherein said means engaging the end plugs and theends of the magnet comprises a pair of coil springs mounted on saidbosslike portions of the end plugs and the bosslike portions of themagnets, said bosslike portions on said plugs and said magnets beingadapted to engage each other and to serve as stops to prevent flatteningof said coil springs.